YANG-CBOR: Allocating SID Ranges for Private Enterprise Number (PEN) Holders
RFC 9997



Internet Engineering Task Force (IETF)                        C. Bormann
Request for Comments: 9997                        Universität Bremen TZI
Category: Standards Track                                      July 2026
ISSN: 2070-1721

  YANG-CBOR: Allocating SID Ranges for Private Enterprise Number (PEN)
                                Holders

Abstract

   YANG-CBOR (RFC 9254, "Encoding of Data Modeled with YANG in the
   Concise Binary Object Representation (CBOR)") defines YANG Schema
   Item iDentifiers (YANG SIDs), globally unique 63-bit unsigned
   integers used to identify YANG items.  RFC 9595 ("YANG Schema Item
   iDentifier (YANG SID)") defines ways to allocate these SIDs using
   IANA registries.

   The present specification employs these SID allocation mechanisms to
   allocate ranges of 100 000 SIDs (representation size 64 bits) to each
   holder of an IANA Private Enterprise Number (PEN) of a value below
   1 000 000.  Holders of PENs of values smaller than 100 000 are also
   allocated ranges of 10 000 SIDs (representation size 32 bits).

Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 7841.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   https://www.rfc-editor.org/info/rfc9997.

Copyright Notice

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   document authors.  All rights reserved.

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Table of Contents

   1.  Introduction
   2.  Example: SID Range Allocation for Holder of PEN 32473
   3.  Discussion
   4.  IANA Considerations
   5.  Security Considerations
   6.  References
     6.1.  Normative References
     6.2.  Informative References
   Acknowledgments
   Author's Address

1.  Introduction

   YANG-CBOR [RFC9254] defines YANG Schema Item iDentifiers (YANG SID),
   globally unique 63-bit unsigned integers used to identify YANG items.
   [RFC9595] defines ways to allocate these SIDs using IANA registries.

   The present specification employs these SID allocation mechanisms to
   allocate ranges of 100 000 SIDs (representation size 64 bits) to each
   holder of an IANA Private Enterprise Number (PEN) of a value below
   1 000 000.  Holders of PENs of values smaller than 100 000 are also
   allocated ranges of 10 000 SIDs (representation size 32 bits).

   IANA has allocated a mega-range with 100 billion SIDs (representation
   size 64 bits) for the SID numbers 300 000 000 000 to 399 999 999 999.

   IANA has also allocated a mega-range with 1 billion SIDs
   (representation size 32 bits) for the SID numbers 3 000 000 000 to
   3 999 999 999.

   PENs are registered in [IANA.enterprise-numbers] using a low-
   threshold, low-overhead registration process.  At the time of writing
   (~38 years after registry creation), around 66 000 PENs are
   registered.  In this document, the registrant for a PEN is referred
   to as the "PEN holder".

   This specification makes the following SID ranges available to
   certain (current or future) PEN holders for allocation in a scheme
   defined by the holder:

   *  The holder of a PEN ppp ppp (< 1 000 000) can use the SID numbers
      3pp ppp p00 000 to 3pp ppp p99 999.

   *  The holder of a PEN pp ppp (< 100 000) can also use the smaller
      SID numbers 3 ppp pp0 000 to 3 ppp pp9 999.

2.  Example: SID Range Allocation for Holder of PEN 32473

   [RFC5612] allocated Enterprise Number 32473 "for use in examples in
   RFCs, books, documentation, and the like".

   If this Enterprise Number had an actual PEN holder, the present
   specification would confer control over the following SID ranges to
   the holder:

   *  3*03 247 3*00 000 up to 3*03 247 3*99 999, and

   *  3 *324 73*0 000 up to 3 *324 73*9 999.

   (The plaintext form of this document shows "*" characters around the
   digits conveying the PEN, which are shown in *boldface* in the other
   renditions.)

   As Enterprise Number 32473 is intended to be used in documentation,
   the SIDs in the two SID ranges are consequently also available for
   use in documentation.

3.  Discussion

   This document assigns two mega-ranges as an extremely-low-threshold
   (zero-interaction) way for a PEN holder to obtain a number space for
   the YANG SIDs used in their YANG modules.  If a PEN is not already
   available to the entity needing such a number space, it can be
   obtained through a very low-threshold process.  However, use of
   values in these mega-ranges is not always the recommended approach
   for a module author:

   *  In the larger of the two spaces, each SID number needs a
      representation size of 64 bits ("64-bit SIDs").  (This larger
      representation size of the absolute value of the SID is of
      comparatively little consequence due to the delta-encoding used
      for SIDs in YANG-CBOR.)

   *  For the holders of PENs with values less than 100 000 in the
      "Private Enterprise Numbers (PENs)" registry, there is another
      smaller space of SID numbers that need a representation size of 32
      bits ("32-bit SIDs").  By or around 2040, the PENs with a value
      less than 100 000 are likely to be exhausted; the expectation is
      that there will be enough opportunities by that time to request
      SID ranges within mega-ranges already allocated by other
      registrants that this mechanism is less needed.

   *  This document does not define infrastructure to discover the YANG
      module behind a SID in one of its ranges.  Of course, each PEN
      holder can provide such infrastructure, but even then the problem
      of how to find that infrastructure for a SID remains.  (Search
      engines may mitigate this somewhat.)  On the other hand, in some
      cases this relative obscurity may be exactly what a PEN holder
      wants to achieve by using this mechanism.

      If obscurity is not the intention, one or both of the following
      approaches are encouraged:

      -  The PEN holder can provide a public repository where their YANG
         models can be found alongside the applicable SID files.  Such a
         repository may be easy to set up using a popular git forge such
         as, at the time of writing, GitHub.

      -  Implementations that employ PEN-based SIDs can facilitate
         information discovery by providing a form of a YANG library
         [RFC8525], possibly a constrained version [core-yang-library].

   Relying on the PEN registry might theoretically trigger a land grab
   of PEN assignments by prospective writers of YANG modules.  However,
   PENs have been around for decades (see Section 3.1.4 of [RFC1065],
   which continues to be in force with no technical changes as
   Section 3.1.4 of RFC 1155 [STD16]), and such a land grab has not
   occurred for the other allocations implicitly provided by obtaining a
   PEN.

4.  IANA Considerations

   As summarized in Table 1, this document allocates the following two
   mega-ranges (Section 6.3 of [RFC9595]) in the "YANG-SID Mega-Ranges"
   registry within the "YANG SIDs" registry group [IANA.yang-sid]:

   *  1 billion SIDs ranging from 3 000 000 000 up to 3 999 999 999
      (32-bit representation size)

   *  100 billion SIDs ranging from 300 000 000 000 up to
      399 999 999 999 (64-bit representation size)

    +=========+=========+============+======+=========================+
    | Entry   | Size    | Allocation | Org  | URL                     |
    | Point   |         |            | Name |                         |
    +=========+=========+============+======+=========================+
    | 3 000   | 1 000   | Private    | IANA | https://rfc-            |
    | 000 000 | 000 000 |            |      | editor.org/info/rfc9997 |
    +---------+---------+------------+------+-------------------------+
    | 300 000 | 100 000 | Private    | IANA | https://rfc-            |
    | 000 000 | 000 000 |            |      | editor.org/info/rfc9997 |
    +---------+---------+------------+------+-------------------------+

      Table 1: YANG-SID Mega-Range Allocations for Use by PEN Holders

   IANA has marked the following ranges as Reserved for Documentation:

   *  303 247 300 000 up to 303 247 399 999

   *  3 324 730 000 up to 3 324 739 999

   An additional contact for the allocation is: IETF CORE Working Group
   (core@ietf.org) or IETF Applications and Real-Time Area
   (art@ietf.org).

   The allocation policy inside the mega-range is "Private" (see
   Section 6.3.2 of [RFC9595]).  The URL is that of the present
   specification.

   The management of each SID block of 100 000 SIDs, ranging from
   3pp ppp p00 000 to 3pp ppp p99 999, is delegated to the PEN holder
   for PEN ppp ppp (i.e., the PEN holder for ppp ppp controls SID
   3pp ppp p00 000 to 3pp ppp p99 999).

   Similarly, the management of each SID block of 10 000 SIDs, ranging
   from 3 ppp pp0 000 to 3 ppp pp9 999, is delegated to the PEN holder
   for PEN pp ppp (i.e., the PEN holder for pp ppp controls SID
   3 ppp pp0 000 to 3 ppp pp9 999).

   Section 6.3.2 of [RFC9595] requires an organization that requests an
   entry in the "YANG-SID Mega-Ranges" registry to ensure the technical
   capacity to manage the SID ranges within those mega-ranges for a
   period of at least 10 years (Private ranges).  The individual SID
   ranges within the mega-ranges allocated in this document are assigned
   through the registration of PEN numbers.  The technical capacity to
   ensure the sustained operation of the PEN number registry is derived
   from the demonstrated capacity of IANA to maintain this registry as
   well as the importance of a functioning PEN number registry in other
   contexts.

5.  Security Considerations

   The Security Considerations of Section 5 of [RFC9595] and Section 8
   of [RFC9254] apply.  In particular, the fact that a certain Private
   Enterprise Number appears in a SID is not an indicator of provenance,
   i.e., it does not guarantee that the SID or underlying YANG model
   actually originates from the holder of that PEN.  The requirement to
   ascertain the authoritative source of this information, as discussed
   in the above security considerations, remains.

6.  References

6.1.  Normative References

   [IANA.enterprise-numbers]
              IANA, "Private Enterprise Numbers (PENs)",
              <https://www.iana.org/assignments/enterprise-numbers>.

   [IANA.yang-sid]
              IANA, "YANG SIDs",
              <https://www.iana.org/assignments/yang-sid>.

   [RFC9254]  Veillette, M., Ed., Petrov, I., Ed., Pelov, A., Bormann,
              C., and M. Richardson, "Encoding of Data Modeled with YANG
              in the Concise Binary Object Representation (CBOR)",
              RFC 9254, DOI 10.17487/RFC9254, July 2022,
              <https://www.rfc-editor.org/info/rfc9254>.

   [RFC9595]  Veillette, M., Ed., Pelov, A., Ed., Petrov, I., Ed.,
              Bormann, C., and M. Richardson, "YANG Schema Item
              iDentifier (YANG SID)", RFC 9595, DOI 10.17487/RFC9595,
              July 2024, <https://www.rfc-editor.org/info/rfc9595>.

6.2.  Informative References

   [core-yang-library]
              Veillette, M. and I. Petrov, "Constrained YANG Module
              Library", Work in Progress, Internet-Draft, draft-ietf-
              core-yang-library-03, 11 January 2021,
              <https://datatracker.ietf.org/doc/html/draft-ietf-core-
              yang-library-03>.

   [RFC1065]  McCloghrie, K. and M. Rose, "Structure and identification
              of management information for TCP/IP-based internets",
              RFC 1065, DOI 10.17487/RFC1065, August 1988,
              <https://www.rfc-editor.org/info/rfc1065>.

   [RFC5612]  Eronen, P. and D. Harrington, "Enterprise Number for
              Documentation Use", RFC 5612, DOI 10.17487/RFC5612, August
              2009, <https://www.rfc-editor.org/info/rfc5612>.

   [RFC8525]  Bierman, A., Bjorklund, M., Schoenwaelder, J., Watsen, K.,
              and R. Wilton, "YANG Library", RFC 8525,
              DOI 10.17487/RFC8525, March 2019,
              <https://www.rfc-editor.org/info/rfc8525>.

   [STD16]    Internet Standard 16,
              <https://www.rfc-editor.org/info/std16>.
              At the time of writing, this STD comprises the following:

              Rose, M. and K. McCloghrie, "Structure and identification
              of management information for TCP/IP-based internets",
              STD 16, RFC 1155, DOI 10.17487/RFC1155, May 1990,
              <https://www.rfc-editor.org/info/rfc1155>.

              Rose, M. and K. McCloghrie, "Concise MIB definitions",
              STD 16, RFC 1212, DOI 10.17487/RFC1212, March 1991,
              <https://www.rfc-editor.org/info/rfc1212>.

Acknowledgments

   This document was inspired by the discussion of the authors of
   [RFC9254] and [RFC9595] on how to handle Rob Wilton's feedback.

Author's Address

   Carsten Bormann
   Universität Bremen TZI
   Postfach 330440
   D-28359 Bremen
   Germany
   Phone: +49-421-218-63921
   Email: cabo@tzi.org